To increase safety by increasing resistance against the injustice unlocking of a lever tumbler lock or a rotary disk tumbler lock.

In this cylinder lock, an implement for copying a commercial key is formed by inserting a flat thin wire into a clearance between the partition plate 3 of the lever tumbler lock and a lever tumbler 11 through a thin pipe inserted into a key hole and the angular position of the unlocking cutout 9 of the lever tumbler is detected to provide a different between keys. A circular arc-shaped projected part 19 about a pivot shaft 12 is formed on at least either of an indoor side surface and the portion of the partition plate 3 opposed to that surface at the free end part of at least one lever tumbler 11, and a circular arc recessed part 21 about the pivot shaft 12 is formed on the other so that the projected part 19 can be engaged with the recessed part 21. Then, the clearance between the partition plate 3 and the lever tumbler 11 is closed by the projected part 19.